In the art of continuous casting of tubular products, it is well-known to utilize a mandrel within a die and to pour molten metal into the die which flows into the space between the mandrel and the die and exits from the bottom of the die as a tubular product with the internal diameter being governed by the diameter of the mandrel. The external diameter of the tubular product is, of course, governed by the internal diameter of the die.
In setting apparatus for a casting operation, a cooler is mounted on a basic support structure or frame and the mandrel, once assembled in and fastened to the die, is placed in the cooler; it being understood that the cooler serves to cool the mandrel and die during casting which takes place at temperatures of approximately 2,200.degree. F. A crucible is then placed above the die on a steel support plate with the die projecting through a bore in the bottom wall of the crucible. Prior to installing the crucible about the die, wet refractory material is applied around the die to form a seal together with refractory material that is later applied after installation of the crucible, between the steel supporting plate which supports the crucible and the crucible itself. A ceramic tundis shell is then placed around the crucible and a cover is placed on the top of the shell to retain heat within the crucible. The set-up is then ready for the prewarming during which time the crucible is heated and the wet refractory sealing material dries to form the desired seal. The prewarming period takes approximately one hour or more.
When the set-up is ready to initiate casting, the molten metal which has been poured into the crucible is at a temperature of approximately 2,200.degree. F. When the molten metal initially enters the die, it engages a starter tip which had been previously positioned in the bottom of the die after installation in the cooler; the starter tip being fixed to the end of an elongated starter bar which projects downwardly from the die between the pinch rolls along the axis of the tubular product to be cast. Subsequently, the starter bar is lowered out of the die followed by the tubular cast product after which the portion of the cast product adjacent the starting bar is severed to remove the starting bar and tip. The casting continues until the desired amount of tubular product has been cast and it is desired to cast another tubular product of a different size or until the life of the die or mandrel ends, such as after approximately fifty (50) hours of continuous casting or if the die or mandrel become damaged.
When it is desired to replace the die and/or mandrel, the casting operation must be stopped, and in most instances the entire set-up allowed to cool to enable removal of the die and mandrel assembly as a unit; it being understood that with methods and apparatus of the prior art, the die and mandrel are usually permanently interconnected or fastened together once they are assembled. Once the set-up has cooled sufficiently, the crucible must be removed from the die requiring disruption of the refractory seal. In addition, the steel support plate over the cooler and under the crucible must be removed in order to permit a replacement die and mandrel assembly to be inserted in the cooler. After the used die is removed from the cooler, the cooler must be allowed to cool after which it must be refaced or sanded in order to provide a proper fit for the replacement die. Once the replacement die and mandrel assembly are inserted in the cooler, the crucible must again be mounted about the die and a new refractory seal applied between the die and the crucible followed by a warming period to bring the crucible up to the proper temperature. It should therefore be seen from the above that replacement of a die or a die and mandrel assembly is a time consuming process which not only lowers production but also involves waste of material and heat energy.
In situations where it is desired to convert a setup from casting a tubular product of one internal diameter to casting a tubular product of the same external diameter but of a different internal diameter, the methods and apparatus of the prior art require that both the mandrel and die once removed, be discarded entirely since they are exposed to oxidation and both united as a one-piece assembly. This is not only costly from the standpoint of wasting the die since the same die may be used for casting tubular products of different internal diameters but having the same external diameter but also, it suffers from the serious drawback that the entire assembly including the crucible, seal, die and cooler must be allowed to cool and then disassembled and then reassembled in the manner indicated above.
The prior art practices referred to above are those which utilize a mandrel supported in and by the die itself with the upper portions of both received in the bottom of the crucible. This die and mandrel assembly and its arrangement within the crucible are to be distinguished from open-ended dies utilized with mandrels such as, for example, disclosed in my U.S. Pat. No. 4,178,982, issued Dec. 18, 1979. In the latter type, the mandrel is not supported by the die but rather by an external structure. Also, the die and mandrel are not received in the crucible because the introduction of the molten metal takes place through the upper open end of the die.